. >> reporter: he spent much of 2002 and 3:00 near kandahar, hunting for taliban. he came back to harvard, but in 2009 with the national guard unit, he went back to afghanistan. >> whoa! >> damn! >> i spent a lot of time with rout clearance units looking for ieds and we got hit several times and vehicles in front of me blown up. my vehicle never got hit. i was very, very lucky. when you run up there and pull open the door and see your injured buddies, you'll never forget that site. >> reporter: this time, back home, he began to explore the science of brain injury. >> what happens when the brain gets hit by a blast wave and slams up against the inside of the skull. >> reporter: with colleagues at northeastern university, parker built new tools to study how a blast affects the brain. it could be years before this leads to new treatments, but parker hopes that eventually will have a broad impact. >> concussions that your favorite football player suffers or the head injury you get when you're in a car accident and your head snaps forward or a shaking baby syndrome. the